<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .list {
      width: 200px;
      height: 150px;
      background-color: aquamarine;
      overflow: auto;
    }
    .news {
      height: 30px;
    }
  </style>
</head>
<body>
  <div id="test"></div>

  

  <script src="../js17/react.development.js"></script>
  <script src="../js17/react-dom.development.js"></script>
  <script src="../js17/babel.min.js"></script>

  <script type="text/babel">
    class NewsList extends React.Component {

      state = {newsArr: []}

      componentDidMount () {
        setInterval (() => {
          const {newsArr} = this.state
          const news = `新闻${newsArr.length + 1}`
          this.setState ({newsArr: [news, ...newsArr]})
        }, 1000)
      }

      getSnapshotBeforeUpdate () {
        return this.refs.list.scrollHeight
      }

      componentDidUpdate (preProps, preState, height) {
        this.refs.list.scrollTop += this.refs.list.scrollHeight - height
      }

      render () {
        return (
          <div className="list" ref='list'>
            {
              this.state.newsArr.map ((item, index) => {
                return <div className='news' key={index} >{item}</div>
            })
            }
          </div>
        )
      }
    }

    ReactDOM.render (<NewsList/>, document.getElementById ('test'))
  </script>
</body>
</html>